For producing low-molecular C2-C4 olefins, in particular propylene, from methanol and/or dimethyl ether (Methanol to Propylene, MTP), a multitude of processes are known to the skilled person, which usually are based on the conversion of an educt mixture containing steam as well as methanol and/or dimethyl ether vapor on a form-selective zeolite catalyst. Such processes are described for example in DE 100 27 159 A1 or EP 0 882 692 B1.
The methanol mostly is introduced into an adiabatically operated prereactor, where it is converted to dimethyl ether (DME) and water (H2O) by using a highly active and highly selective Al2O3 catalyst. The methanol/water/DME stream is passed to the first one of a plurality of reactor stages, into which the vapor produced is supplied as well. In this reactor stage, an almost complete conversion of both methanol and dimethyl ether occurs, with propylene chiefly being obtained as hydrocarbon product. Further conversions can be achieved in subsequent reactor stages. In all stages, the process conditions are chosen such that similar reaction conditions and a maximum propylene yield are ensured. Thus, a yield of propylene of more than 60% is obtained, and in addition further olefin fractions above all, but also a gasoline fraction are obtained.
The gasoline product resulting from such a plant is of high value. Typical values as compared with the indicated European specifications according to EN 228 for regular gasoline reveal the high value of the product:
EN 228 (regularPropertyAchieved propertygasoline)Octane number93-95>91(ROZ, RON)Sulfur content<detection limit<50 mg/kgAromatics content15-20 vol-%<35 vol-%Benzene content<0.25 vol-% <1 vol-%
However, the direct use of this gasoline at the gasoline station still is not possible, since the olefin content lies above the limit value of maximally 18 vol-% valid in Europe.
From the prior art, a number of solution possibilities for this problem are known, by means of which the olefin content can be reduced.